1. Field of the Invention
The present invention relates to a vehicular power supply apparatus in which a capacitor is used, and which is applied to a vehicle having an idling stop function that automatically stops an engine when the vehicle is at a halt.
2. Description of the Related Art
In recent years, many vehicles having idling stop functions have been put to practical use. With the idling stop functions, when the vehicles stop at intersections or the like, their engines are automatically stopped, and their engines are restarted in conjunction with drivers' preset driving operations. In order to improve engine startability, it is common that a power supply of a vehicle having an idling stop function of the above type has a configuration in which both a battery, such as a lead-acid battery, and a capacitor, such as a lithium ion capacitor or an electric double layer capacitor, are used to supply a large current to an engine starter.
Accordingly, to maintain good engine startability, it is essential to maintain capacitor performance. For example, Japanese Unexamined Patent Application Publication No. 2003-224902 discloses, as a technology for performing a capacitor abnormality diagnosis, a technology in which changes in current and voltage for a capacitor are measured, and, when the capacitance or internal resistance of the capacitor calculated on the basis of the measured values are outside an allowable range, it is determined that the capacitor is abnormal.
In the technology disclosed in Japanese Unexamined Patent Application Publication No. 2003-224902, it is necessary to provide each capacitor with a dedicated voltage sensor or the like, so that there is a possibility of structural complexity.